1.Field of the Invention
The present invention relates to a wireless mobile communication system. More particularly, the present invention relates to a handover system and method in a wireless mobile communication system.
2.Description of the Related Art
For the next generation wireless mobile communication system, research is being conducted to provide users with high-speed services having various Quality of Service (QoS) classes. An exemplary next generation wireless mobile communication system includes a communication system based on Institute of Electrical and Electronics Engineers (IEEE) 802.16.In the next generation wireless mobile communication system, a Mobile Station (MS) can handover from its current cell to another cell.
FIG. 1 is a signaling diagram illustrating a conventional handover procedure in a wireless mobile communication system.
Referring to FIG. 1, an MS 100 determines if a condition to initiate handover has been satisfied, and when the condition is satisfied, the MS sends a handover request message (that is, Mobile MS Handover Request (MOB_MSHO-REQ) message) to a Serving Base Station (BS) (hereinafter referred to as ‘SBS’) 110 in step 101. It will be assumed herein that the MS 100 considers a Target BS1 (hereinafter referred to as “TBS1”) 120 and a TBS2 130 as its handover target BSs. Therefore, the MOB_MSHO-REQ message includes therein information indicating TBS1 and information indicating TBS2. The TBS indication information can be an Identifier (ID) of its associated TBS.
The SBS 110 sends a HO-request message indicating the handover request of the MS 100 to each of the TBS1 120 and the TBS2 130 in steps 103 and 105.
The TBS1 120 and TBS2 130 each send a HO-response message, or response message to the received HO-request message, to the SBS 110 in steps 107 and 109. It is assumed herein that the TBSs are BSs that can accept the handover of the MS 100.
The SBS 110 sends to the MS 100 a handover response message (that is, Mobile BS Handover Response (MOB_BSHO-RSP) message) including information on the TBSs and Cipher-based Message Authentication Code (CMAC) information for message authentication in step 111. The CMAC can be determined herein as a different value according to the generated frame. In addition, the SBS 110 sends a Handover Acknowledgement (HO-ACK) message indicating its receipt of the HO-response message to each of the TBS1 120 and TBS2 130 in steps 113 and 115.
After determining a BS to which it intends to perform a handover, the MS 100 sends a handover indication message (that is, Mobile Handover Indication (MOB_HO-IND) message) including information on the determined BS and CMAC information to the SBS 110 in step 117. It is assumed herein that the MS 100 has selected the TBS2 130 as its handover target BS.
The SBS 110 sends to the TBS2 130 a HO-confirm message indicating that the MS 100 will soon handover thereto in step 119. Thereafter, the SBS 110 transfers context information of the MS 100 to the TBS2 130 in step 121.
The TBS2 130 sends a HO-ACK message indicating its receipt of the context information, to the SBS 110 in step 123.
The MS 100 sends a ranging code to the TBS2 130 in order to perform ranging with the TBS2 130 in step 125. The TBS2 130 sends a Ranging Response (RNG-RSP) message to the MS 100 in step 127. The RNG-RSP message is used for allocating resources so that the MS 100 can send an uplink Ranging Request (RNG-REQ) message. Therefore, the MS 100 sends an RNG-REQ message to the TBS2 130 using the allocated uplink resources in step 129. The RNG-REQ message includes CMAC tuple information.
The TBS2 130 sends an authentication request for the CMAC tuple to an authentication station 140 in step 131. The authentication station 140 generates an Authentication Key (AK) in step 133, and sends to the TBS2 130 an authentication response message including the generate AK information, i.e., AK context and Security Association (SA) information in step 135.
The TBS2 130 verifies the CMAC of the MS 100 in step 137, and when the CMAC is valid, sends an RNG-RSP message to the MS 100 in step 139. The RNG-RSP message includes a HO process optimization field and CMAC information. In addition, the TBS2 130 sends a confirm message for the authentication response message to the authentication station 140 in step 141. Thereafter, a data exchange is made between the MS 100 and the TBS2 130.
As described above, the TBS, to which the MS intends to perform a handover, should determine the correctness of a CMAC value of the MS after receiving authentication information from the authentication station. This means it is necessary to perform the same verification process for both a case where the TBS receives a normal RNG-REQ message from the MS and a case where the TBS receives a wrong RNG-REQ message. Therefore, resources needed for the verification may be wasted. In particular, when a plurality of MSs send incorrect messages after their intentional manipulation, the resources such as frequency resource, time resource and memory resource can be wasted.